Optical viewing apparatus such as surgical microscopes or endoscopes are often not provided only for conventional viewing of the viewed object but are also used, for example, to carry out a fluorescence measurement. For this purpose, the optical viewing apparatus includes a fluorescent light source which emits a wavelength suitable for exciting fluorescence in the viewed object. In conventional optical viewing apparatus, high power white light sources are often used, that is, broadband light sources which are driven at maximum power for fluorescence excitation. In this connection, over 99% of the electric power of the high power white light source is converted into heat which must be conducted away. In addition, the radiation intensity can, however, be too weak for weak fluorescence or deep surgical channels. Furthermore, the operation of a high power white light source at maximum power leads to a stress on the patients which, in turn, can lead to the situation that the fluorescence operation must be limited with respect to time. An endoscope having a white light source, which is used as a fluorescence light source, is described, for example, in U.S. Pat. No. 6,510,338.
In addition to the use of white light sources as excitation light sources for fluorescence, the use of light diodes or lasers as excitation light sources are also known.
A surgical microscope is described in United States patent publication 2006/0232855 wherein the fluorescence radiation is not generated with a white light source but with a semiconductor laser. This laser light is coupled into the illuminating beam path of the microscope below the main objective.
In published United States patent application 2005/0152029, a fluorescence microscope is described which includes an incandescent lamp for transmissive illumination of the object and a light diode as an excitation light source for fluorescence radiation. The light of the light emitting diode (LED) is coupled into the illuminating beam path above the main objective.
United States published patent application 2005/0224692 discloses a fluorescence microscope having a fluorescence light source based on several light emitting diodes.
German utility model registrations 20 2004 010 121 U1 and 20 2006 000 018 U1 describe the use of light emitting diodes as fluorescence light sources in microscopes.